This is merely dinosaurs that were brought back to life using dna and artificial womb technology by the highly advanced pre-flood Atlantean civilization. Thats why theres still soft tissue its only a few tens of thousands of years old and was frozen!

you also have to consider that curious aliens could have studied our planet some time in the last 100k years and collected dinosaur dna using their far more advanced and effective methods, and bought them back "jurassic park style" to study them whilst they were waiting for their mothership to come back around to pick them up a few years later and then abandoned the earth to go study other planets.